Prosser, Wash.—An early cold front that swept across the Northwest last November yielded the second-earliest ice wine harvest on record in British Columbia, but grapegrowers in Washington state are still wondering what effect it had on their vines.

Many growers are reporting significant damage, but a chilly spring has delayed bud break and accurate answers to the questions that vineyard managers are asking.

“We don’t know what the aftermath will be, because we haven’t seen bud break yet in most places. And for most growers, it’s been so irregular, so non-uniform in terms of where damage occurred and how much,” Markus Keller, a researcher and Chateau Ste. Michelle distinguished professor of viticulture at Washington State University’s Irrigated Agriculture Research and Extension Center in Prosser, told Wines & Vines this week.

Keller explained that last year’s cool fall weather should, if anything, have helped vines shut down as the days grew shorter. Under normal circumstances, conditions were right for a steady senescence and hardening off of the vines.

But when some areas were hit with temperatures as low as 0°F in late November, it was too much too soon. “It wasn’t absolutely that cold, but it was too early,” Keller said. “The vines hadn’t fully acclimated yet when it happened.”

Still, damage was variable: Keller spoke to growers last week who indicated their losses could be anywhere from zero to 100%. Vineyards in the Yakima Valley appear to be unscathed, while many in the Horse Heaven Hills were hit hard. A year-end review of the industry by Northwest Farm Credit Services suggested that upward of 20% of vineyard acreage could see “significant damage” but deferred a definitive statement until bud break this spring.

With light snow persisting into April, spring is off to a slow start. Growers contacted by Wines & Vines indicated delays of up to two weeks in bud break. Growing-degree days, calculated from WSU AgWeatherNet stations, numbered just 10 on April 24, compared to a long-term pattern of 68 days. While two weeks isn’t much at this stage of the season, it’s got growers wondering how their vines will respond.

Still time to catch up
“I can imagine that this cool spring and consequential delayed bud development is prolonging the suspense of growers waiting for bud break,” said Tedd Wildman, a partner at Stone Tree Vineyard on the Wahluke Slope near Mattawa.

While his vines have negligible damage from the November cold snap, he is seeing variable bud swell that heralds challenges in getting varieties such as Syrah to ripen uniformly later this year. Wildman is not otherwise concerned about the harvest: The vines have lots of time to catch up, he believes.

Kevin Corliss, director of vineyard operations for 1.5 million-case Chateau Ste. Michelle Wine Estates, also is optimistic. His examination of vineyards indicates that the youngest vines have been hardest hit (which isn’t unusual when extreme cold weather hits). Older vines are merely delayed.

But sap is flowing and buds are swelling, even if the jury’s still out. “Bottom line is that we're still waiting—a bit more impatiently now.” he said.

Whether warm weather materializes later this season is another question. Speaking to growers at the Oregon Wine Industry Symposium in February, climate expert Dr. Greg Jones forecast a growing season for 2011 not unlike what the Northwest experienced in 2010.

While minimum temperatures during the 2010 growing season were largely unchanged, Jones pointed out that maximum temperatures were well below the historical average. This year, he expects a cool summer to follow what he described in February as a cool, wet spring with a moderate increase in spring frost risk. Many areas of the Northwest now accept those conditions as a fact rather than a forecast.

Wildman, for his part, feels the cool spring weather is ideal medicine for any damaged vines. “A long cool spring following a serious cold weather event is most conducive for vine self-repair and future vintages,” he said. “Vines have an incredible ability to heal themselves and outperform negative expectations.  I suspect many growers will find that their vines are in better shape than they thought.”